This invention relates to liquid filtration, and more particularly to the removal of contaminants from environmental water. "Environmental Water" refers to any water effected by human activities destined for discharge into the environment.
Storm water runoff has been identified as the largest source of surface water quality degradation in the United States. Storm water carries the contaminants it picks up into streams, lakes, rivers, oceans and ground water aquifers. To prevent such contaminants from impairing the quality of the water and sediments in such bodies, it is necessary that the storm water runoff contaminants be removed, or at least reduced, and governmental agencies are increasingly requiring treatment to accomplish this goal. Industrial and urban storm water runoff typically contains heavy metals, oils and suspended sediments. The "first flush" or initial runoff generated by a storm usually contains the majority of the contaminants.
When storm water runoff is treated, it is usually collected in above-ground facilities and treated by chemical precipitation, clarification, biological treatment, or filtration. Treatment in such facilities is expensive. It is especially difficult to remove fine particles which are generally less than 500 microns in size without very expensive filtration. It is therefore highly desirable that as many contaminants as possible should be removed from the runoff by preliminary filtration before the runoff gets into a sewer system or body of water. However, the only contaminant removal technique used commonly today is catch basin detention employing filter fabric such as geotextiles. Generally these fabrics tend to catch particles larger than 500-1000 microns, and they rapidly become clogged when the runoff contains oils or fine sediments. However, in most storm water discharges, particles smaller than 500-1000 microns and oil and grease usually are or contain the majority of the contaminants and are therefore the primary sources of water pollution.